To identify mutations in the gene(s) which cause familial pituitary tumors. Molecular genetic analysis will be used to identify chromosomal regions which are coinherited by family members with pituitary tumors (linkage analysis). Can-didate genes in the mapped region will be screened for mutations. These studies will prove enormously beneficial by allowing individuals who inherit an at-risk chromosome to undergo early screening/detection/treatment, releiving anxiety for those not at risk, and developing therapeutic interventions.